/* 
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;

using IndexReader = Lucene.Net.Index.IndexReader;

namespace Lucene.Net.Search.Function
{
    
    /// <summary> Expert: source of values for basic function queries.
    /// <p/>At its default/simplest form, values - one per doc - are used as the score of that doc.
    /// <p/>Values are instantiated as 
    /// <see cref="Lucene.Net.Search.Function.DocValues">DocValues</see> for a particular reader.
    /// <p/>ValueSource implementations differ in RAM requirements: it would always be a factor
    /// of the number of documents, but for each document the number of bytes can be 1, 2, 4, or 8. 
    /// 
    /// <p/><font color="#FF0000">
    /// WARNING: The status of the <b>Search.Function</b> package is experimental. 
    /// The APIs introduced here might change in the future and will not be 
    /// supported anymore in such a case.</font>
    /// 
    /// 
    /// </summary>
    [Serializable]
    public abstract class ValueSource
    {
        
        /// <summary> Return the DocValues used by the function query.</summary>
        /// <param name="reader">the IndexReader used to read these values.
        /// If any caching is involved, that caching would also be IndexReader based.  
        /// </param>
        /// <throws>  IOException for any error. </throws>
        public abstract DocValues GetValues(IndexReader reader);
        
        /// <summary> description of field, used in explain() </summary>
        public abstract System.String Description();
        
        /* (non-Javadoc) <see cref="java.lang.Object.toString() */
        public override System.String ToString()
        {
            return Description();
        }
        
        /// <summary> Needed for possible caching of query results - used by <see cref="ValueSourceQuery.Equals(Object)" />.</summary>
        /// <seealso cref="Object.Equals(Object)">
        /// </seealso>
        abstract public  override bool Equals(System.Object o);
        
        /// <summary> Needed for possible caching of query results - used by <see cref="ValueSourceQuery.GetHashCode()" />.</summary>
        /// <seealso cref="Object.GetHashCode()">
        /// </seealso>
        abstract public override int GetHashCode();
    }
}